Process for the manufacture of alkali hydroxides and apparatus for carrying out reactions



Jan. 1, 1946. G. E. EDWARDS 2,392,235

PROCESS FOR THE MANUFACTURE OF ALKALI HYDROXIDES AND APPARATUS FORCARRYING OUT REACTIONS Filed July 9, 1941 INVENTOR. GEORGE ERNESTEDWARDS,

BY'K y Patented Jan. 1,

PROCESS FOR THE MANUFACTURE OF AL- KALI HYDROXIDES AND APPARATUS FOR ICARRYING OUT REACTIONS George Ernest Edwards, Runcorn, England, as-,

signer to Imperial Chemical Industries limited, a corporation of Great 1Application July 9, 1941, sci-a1 No. 401,686

In Great Britain August 28, 1940 11 Claims. I (CI. 23-48!) v Thisinvention relates to improvements in processes and apparatus forcarrying out reactions involving liquid amalgams, that is to say,solutions or liquid alloys of metals in mercury; 1 and especially forcarrying out reactions between liquid alkali metal amalgams and aqueoussolutions.

Various processes are known in which alkali metal amalgams are treatedwith aqueous solutions so as to cause the alkali metal in the amalgam toreact with the solution. Thus amalgams may be used in this way forreducing aqueous solution of organic compounds, for reducing sulphitesto'hydrosulphites, and for reducing alkali metal polysulphides tosulphides. One type of apparatus used for contacting a liquid amalgamwith a solution comprises a trough having a slightly sloping bottom overwhich the amalgam flows either co-current or counter-current to theaqueous solution. Such an apparatus enables the reaction to be carrieding from the said upper edge at least down to the level of the amalgamin the trough on the one hand, and on the other hand .downwards alongout efficiently but has the disadvantage that it occupies a large floorspace in comparison with its output, and for .this reason many attemptshave been made to devise an apparatus in which the flow of amalgam is sbstantially vertical; thus it has been proposed (so flow the amalgamdownvertical sheets or hands of a. metal such.

as iron, immersed inthe'aqueous-solution. 1 with such arrangements,however, difllculties have been experienced in maintaining an even flowl of amalgam to the supporting surfaces; slight irregularities in thesupply. from point to point,

the supporting surface each to the same level below that of the amalgamin the trough.

By this means, the rate at which amalgam travels along the severalpassages is determined by the difference in hydrostatichead between thelevel at which these passagesterminate on the supporting surface, andthe level of the amalgem in the trough. Once the formerlevel has beenfixed, as will be done when the apparatus for carrying out the processis setup, the head for tageously created by making use of the capillaryattraction between the amalgam and adjacent surfaces of metal members ofa small cross-section. e. g., of metal wires or strips. ber ofamalgamated wires or strips may be arranged over the edge of thesupporting surface and of the trough and the amalgam level in the troughadjusted to be high enoughfor the amal gam to rise between the wires asthe result of surface tension to the edge of the trough and to flowthence down between the adjacent wires to output vi and efliciency.-Such diiilculties have I been largely responsible for the fact that novertical apparatus of this yp has achieved commercial success in spiteof the advantages which it would possess in'respect of saving ofmercury, economy of floor space and compactness of si n. I

1 According to the present invention in carrying out reactions involvingliquid amalgams in which amalgam is caused to flow downwards over avertical or steeply sloping supporting surface wetted by the amalgam,irregularities in thesupply of amalgam thereto are largely obviated bysiphon- .18- the liquid amalgam over the upper edge of the supportingsurface. Capillary attraction will then maintain acoating of amalgambetween adiacent wires or strips and enable amalgam to travel under theinfluence of the hydrostatic head.

to the supporting surface. Advantageously, a plurality of amalgamatedwires are provided in close proximity to each other and to anamalgamated metal surface, whereby capillary attraction 1 way.

will cause amalgam tobe held between adjacent wires-and between thewires and the metal sur- I face and provide the necessary passage inthat es-., water) a supporting surface the liquid With'such anarrangement a greater voladjacent surfaces.

gain extending downwards in the said tank, -a trough having one edgesubstantially coincident with the upper edge ofthe said surface,- meansfor supplying liquid amalgam to the trough, means for regulating thelevel of amalgam in the trough, means for maintaining a reactive fluidin contact with the said surface, capillary channels for transferringamalgam from the trough to the said surface formed by a plurality ofamalgamated metal members of small cross section, disposed at intervalsalong the said edge of the trough and extending on the one hand downinto the trough and on the other hand down each to substantially thesame level on the supporting surface below the level at which theamalgam in the trough is maintained. Suitably the members are wires ortapes. They may be placed sufliciently close together for the spacesbetween adjacent members to form the capillary channels; advan- 2oformed between the members and the said sur-f convex curve over the edgeof the trough. The 5' height of the top of this curve above the level ofthe amalgam in the trough should not exceed the distance up which theamalgam can be drawn by capillary attraction between two adjacentsurfaces of the metal used to make the feeding device and this willdepend on the distance between With very small separation the distancewill be large, but then because of frictional forces the rate of flow ofthe amalgam tends to become too small for practical purposes. Usingamalgamated iron, the height of the curve above the level of the amalgamshould not be more than about one-fourth inch. Thus-in one form of theinvention the apparatus comprises a deep tank having near the topmaintained in the trough. By adjusting this weir the level can bealtered to any. suitableposition.

part of the surface of theiron sheet. Suitably wires are used which are,e. g., 0.1 to 0.05 inch in diameter and are spaced apart by a distance Iof the same order. The narrow spaces formed 5 between the plane surfacesof the trough or iron sheet and the cylindrical surfaces of the wiresthen act as capillaries up which the amalgam will be drawn when it issupplied to the trough up to a suitable level. The sheet is suitablysupported with the amalgam. An outlet for the reacted solution is alsoprovided in the upper part of the tank, preferably above the level ofthe amalgam tro'ugh.. a

If desired, a number of troughs can be arranged in parallel close to.each other in the same apparatus, each trough having a correspondingmetal sheet and set of wires and being provided with means for supplyingamalgam. In

this way a compact apparatus with a comparatively large capacity isobtained.

Priorto putting the apparatus into operation the surfaces of the ironsheet and wires are thoroughly cleaned and amalgamated by any suitablemeans.

In usuing the apparatus the circulation of aqueous solution through thetank is set up and amalgam is delivered to the trough until the level ofthe amalgam is not more than one-fourth inch below the lower edge ofthetrough. It is then drawn by capillary attraction between the wires andthe amalgamated iron surfaces and thus is delivered to the downwardlyextending.

surface of the iron sheet where it has ample opportunity to react withthe aqueous solution during its passage to the bottom of the, sheet.-The supply of amalgam is maintained at such-a rate that denudation ofthe mercury is substantially complete by the time it has travelled tothe bottom of the tank. In practice it is found that a considerablevariation in the .rate of flow of the amalgam is possible while stillmaintaining a suitable level in the trough, and thusno difficulties. areencountered in settingup a flow which enables denudation to besubstantially complete when the denuded amalgam reaches the bottomof thetank and at the same timemain- One side of the trough is'preferablyhigher than the other to prevent amalgam seeping up over it,

and from the outside of the lower edge or lip an iron sheet of widthapproximately equal to the length of the trough extends downwards to thelower part of the tank to form the, surface onthe other side they lieclosely along the upper 75 A. number of iron wires tains a suitablelevelof amalgam.

. In the accompanying drawing there is shown be more readily seen; forthe sake of simplicity only a few or the wires have been shown inposition and .the weir and means for supplying liquid amalgam to thetrough and for regulating its level have been omitted. The tank and thelower part of the iron. sheet have also been omitted for the sake ofsimplicity.

In this diagram,- the trough has a'forward side 2 which is slopedinwards to form a' sloping face 3, the thickness 'of' this'sloping sideof the trough forming a second sloping face 4 at right angles to it. Therear side 5 of the trough extends ver tically upwards higher than theedge formed by.

.- the join or faces-3 and 4. From thelower edge of face v3 a steeplyinclined iron sheet 8 extends downwards into the reaction tank (notshown).

1 (a feworly are shown) i escapes equal to their diameter, parallel tothe lines of greatest slope of sheet 8, and faces 3 and l touching thesesurfaces, they are kept in position by a retaining member 8. The ends ofthe wires within the trough are approximately at the lower edge of faceI, and the second endof each wire is at the same level on sheet I, whichlevel is below that of the lower edge of face I. i

In operation the faces 3 and l and sheet- 8 are' amalgamated, and liquidamalgam is supplied to trough I so as to maintain th surface 8 at such adistance below the loin-of faces 3 and! that having a maintained leveland then to flow downwardly in open closely adjacent paths longer thanthe rising paths onto a continuous receiving surface arranged forgravity flow.

' 3. An apparatus for feeding a liquid to a reaction zone comprising atrough adapted to contain a liquid at a maintained level therein, .asurthe amalgam can rise by capillary attraction in the narrow passagesbetween the wires I and face 4 to the join. Having reached this level,the amalgam will flow down the narrow passages between wires .1 and face3, the wires I and sheet 8, and the diflerence in hydrostatic headbetween the ends of wires 1 on sheet 6 and the i'ree surface 9 of theamalgam in the trough will ensure the continuous flow of amalgam alongthese passages. The hydrostatic head is the same for all the wires andthus an equal supply of amalgam is delivered to the sheet 6 from each ofthem,

, and thus an equal supply along the whole of the width of the sheet. 1

Although in the above description the manufacture of a particularproduct has not been mentioned it will be realised that the methods maybe applied to-any suitable-reaction. Thus the method and apparatus mayvery conveniently :be applied to the manufactured alkali metalhydroxidesby reacting a liquid alkali metal amalgam-with water, or to themanufacture of alkali metal sulphides by reacting an alkali metalamalgam with a solution of the corresponding alkali metal polysulphide;similarly aqueous solutions of organic compounds may be reduced, orsulphites may be reduced to the. corresponding hydrosulphites.

In my copending applicationSerial No. 401,687, filed July 9, 1941, thereis described a process and apparatus for carrying out reactionsinvolving a liquid alkali metal amalgam with an aqueous liquid, byallowing the amalgam to flow down the surfaces of a plurality of spaceddownwardly extending metal members of small cross-section;

'. advantageously the amalgam is fed to the members from a vessel, e..g., a trough, over one edge of which the members pass into the amalgamso that capillary channels for the amalgam are formed between adjacentmembers and between adjacent members and the sides of the trough, alongwhich amalgam can be fed from the vesselto the downwardly extendingmembers. The present application is primarily concerned with the methodof feeding the amalgam from the 'capillary ch'annels disposed side by'side and closely spaced laterally from each other, and dellvering' theamalgam from said channels to a receiving surface arranged for gravityflow.

, 2. The process of submitting a liquid amalgam to reaction conditions,which comprises causing it to rise by capillary action in a plurality ofclosely adjacent openpaths from a body thereof face wettable by theliquid having an upper edge near said trough and extending downwardlyinto the reaction zone, and a plurality of independent capillarypassages uniformly spaced across said edge and leading from below saidlevel upwardly over said edge and downwardly onto said surface.

4. An apparatus as defined in claim 3 wherein said capillary passagesare formed by a plurality of amalgamated metal members of relativelysmall cross section disposed in substantially closely lat erally spacedrelationship throughout their effective length. v I r 5. An apparatusfor feeding a liquid to a re-, action zone comprising a trough having aside terminating upwardly in a horizontal edge, a plurality ofmembersextending upwardly from said trough over said edge and downwardlyoutside the trough,'and a continuous surface' in con tact with the saiddownwardly extending portions of said members and itself extendingdownwards into the reaction zone, said members being of such length,small cross-sectional area and relationship that liquid will be causedto flow between adiacent members from a maintained level in said troughonto said surface. for continued flow thereon.

as 6. An apparatus for feeding a liquid to a reaction zone comprising 'atrough, a portion thereof which defines an upper horizontal edge of saidtrough forming part of a continuous surface structure extending upwardlyfrom within said trough 40 over said horizontal upper edge anddownwardly therefrom, said surface being prolonged downwardly withinsaid reaction zone, a plurality of members lying on said surfaceextending parallel to each other from within said trough over saidedge'and terminating on the downward extension thereof, said members andsaid surface being wettable by the'liquid and said members being of suchlength, small cross-seetiona1 area, and relationship that liquid willflow from a maintained level in said trough onto said surface forcontinued gravity flow thereon.

7. An apparatus for feeding a liquid from an open vessel adapted tocontain the same at a maintained level comprising a plurality ofsideby-side elongated members of small cross-sectional area extendingupwardly from below the said level in said vessel to a point above thatlevel and then downwardly outside the vessel to below said level, saidmembers being disposed closely together so as to" define capillarypassages between them, a surface underlying said members and in contacttherewith and extending downwardly to a reactionzone, said members andsaid surface being wettable by the liquid and the extent of said membersabove said level being such that capillary attraction will cause liquidto rise over the highest point thereof to flow by gravity along thedownwardly extending portion thereof.

8. An apparatus for feeding a liquid-to a reaction zone comprising 'atrough adapted to containthe liquid at a maintainedlevel, said trough.having a portion'which defines an upper horizontal edge and forms partof a continuou surface extending upwardly from within'said trough oversaid edge and downwardly therefrom, said and terminatingon the downwardportion of said -members above said level being such that capilsurfacebeing prolonged downwardly into said reaction zone, a plurality ofmembers lying on said surface extending parallel to each other from be-vi low the said level in said trough over said edge surface below thesaid level, said members being of such small cross-sectional area and insuch adjacent relationship, and the extent of said lary action willcause liquid to rise between adia-' cent members over the highest pointthereof to flow by gravity down said surface to the reaction zone.

9. An apparatus for feeding a liquid to a reaction zone comprising atrough having a portion which defines an upper horizontal edge of saidtrough and forms part of a continuous surface structure extendingupwardly from within said trough over said horizontal edge anddownwardly therefrom, said surface being prolonged downwardly withinsaid reaction zone, means for maintaining the liquid in the trough at apredetermined levelbelow said edge, a plurality of members lyingreactive fluid which comprises in combination a tank, the lower part ofwhich constitutes a reaction zone, a trough in the upper part of thetank having a side terminatingupwardly in a horizontal edge, a pluralityof members extendingupwardly from said trough over said edge anddownwardly outside the trough, and a continuous surface in contact withthe said downwardly extending portions of said members and itselfextending v downwardly into the reaction zone, said members and saidsurface being wettable by the liquid and said members being ofsuchlength, small cross-sectional area and relationship that'liquid r willflow between adjacent members from-a maintained level in said troughonto said surface for continued flow thereon. v

11. An apparatus for reacting a liquid with a reactive fluid comprisingin combination a tank, the lower part of which constitutes the reactionzone, a trough in the upper part of the tank, a continuous surfaceextending upwardly from within said trough, across an edge of the troughand downwardly outside of the trough into said reaction zone, aplurality of members lying on said surface extending parallel to eachother from within said trough and terminating on the downward extensionof said surface, means for supplying liquid to the said trough, andmeans for maintaining the liquid therein at such a level that liquidwill rise by capillary action along and be- GEORGE ERNEST EpwARns.

